# Unfortunately we need to require multipart_progress here and not in 
# uplaod_status_for because if the upload happens to hit a fresh FCGI instance
# the upload_status_for method will be called after the CGI object is created
# Requiring here means that multipart progress will be enabled for all multipart
# postings.
require 'action_controller/cgi_ext/multipart_progress'

module ActionController #:nodoc:
  # == THIS IS AN EXPERIMENTAL FEATURE
  #
  # Which means that it doesn't yet work on all systems. We're still working on full
  # compatibility. It's thus not advised to use this unless you've verified it to work
  # fully on all the systems that is a part of your environment. Consider this an extended
  # preview.
  #
  # == Action Pack Upload Progress for multipart uploads
  #
  # The UploadProgress module aids in the process of viewing an Ajax driven
  # upload status when working with multipart forms.  It offers a macro that
  # will prepare an action for handling the cleanup of the Ajax updating including
  # passing the redirect URL and custom parameters to the Javascript finish handler.
  #
  # UploadProgress is available for all multipart uploads when the +upload_status_for+
  # macro is called in one of your controllers.
  #
  # The progress is stored as an UploadProgress::Progress object in the session and
  # is accessible in the controller and view with the +upload_progress+ method.
  #
  # For help rendering the UploadProgress enabled form and supported elements, see
  # ActionView::Helpers::UploadProgressHelper.
  # 
  # === Automatic updating on upload actions
  #
  #   class DocumentController < ApplicationController   
  #     upload_status_for  :create
  #     
  #     def create
  #       # ... Your document creation action
  #     end
  #   end
  #
  # The +upload_status_for+ macro will override the rendering of the action passed
  # if +upload_id+ is found in the query string.  This allows for default
  # behavior if Javascript is disabled.  If you are tracking the upload progress
  # then +create+ will now return the cleanup scripts that will terminate the polling
  # of the upload status.
  #
  # === Customized status rendering
  #
  #   class DocumentController < ApplicationController   
  #     upload_status_for  :create, :status => :custom_status
  #     
  #     def create
  #       # ... Your document creation action
  #     end
  #
  #     def custom_status
  #       # ... Override this action to return content to be replaced in
  #       # the status container
  #       render :inline => "<%= upload_progress.completed_percent rescue 0 %> % complete", :layout => false
  #   end
  #
  # The default status action is +upload_status+.  The results of this action
  # are added used to replace the contents of the HTML elements defined in
  # +upload_status_tag+.  Within +upload_status+, you can load the Progress
  # object from the session with the +upload_progress+ method and display your own
  # results.  
  #
  # Completion of the upload status updating occurs automatically with an +after_filter+ call to
  # +finish_upload_status+.  Because the upload must be posted into a hidden IFRAME to enable
  # Ajax updates during the upload, +finish_upload_status+ overwrites the results of any previous
  # +render+ or +redirect_to+ so it can render the necessary Javascript that will properly terminate 
  # the status updating loop, trigger the completion callback or redirect to the appropriate URL.
  #
  # ==== Basic Example (View):
  #
  #  <%= form_tag_with_upload_progress({:action => 'create'}, {:finish => 'alert("Document Uploaded")'}) %>
  #  <%= upload_status_tag %>
  #  <%= file_field 'document', 'file' %>
  #  <%= end_form_tag %>
  #
  # ==== Basic Example (Controller):
  #
  #  class DocumentController < ApplicationController
  #    upload_status_for :create
  #
  #    def create
  #      @document = Document.create(params[:document])
  #    end
  #  end
  #
  # ==== Extended Example (View):
  #
  #  <%= form_tag_with_upload_progress({:action => 'create'}, {}, {:action => :custom_status}) %>
  #  <%= upload_status_tag %>
  #  <%= file_field 'document', 'file' %>
  #  <%= submit_tag "Upload" %>
  #  <%= end_form_tag %>
  #
  #  <%= form_tag_with_upload_progress({:action => 'add_preview'}, {:finish => 'alert(arguments[0])'}, {:action => :custom_status})  %>
  #  <%= upload_status_tag %>
  #  <%= submit_tag "Upload" %>
  #  <%= file_field 'preview', 'file' %>
  #  <%= end_form_tag %>
  #
  # ==== Extended Example (Controller):
  #
  #  class DocumentController < ApplicationController
  #    upload_status_for :add_preview, :create, {:status => :custom_status}
  #
  #    def add_preview
  #     @document = Document.find(params[:id])
  #     @document.preview = Preview.create(params[:preview])
  #     if @document.save
  #       finish_upload_status "'Preview added'"
  #     else
  #       finish_upload_status "'Preview not added'"
  #     end
  #    end
  #
  #   def create
  #     @document = Document.new(params[:document])
  #
  #     upload_progress.message = "Processing document..."
  #     session.update
  #
  #     @document.save
  #     redirect_to :action => 'show', :id => @document.id
  #   end
  #
  #   def custom_status
  #     render :inline => '<%= upload_progress_status %> <div>Updated at <%= Time.now %></div>', :layout => false
  #   end
  module UploadProgress
    def self.append_features(base) #:nodoc:
      super
      base.extend(ClassMethods)
      base.helper_method :upload_progress, :next_upload_id, :last_upload_id, :current_upload_id
    end

    module ClassMethods #:nodoc:
      # Creates an +after_filter+ which will call +finish_upload_status+
      # creating the document that will be loaded into the hidden IFRAME, terminating
      # the status polling forms created with +form_with_upload_progress+.
      #
      # Also defines an action +upload_status+ or a action name passed as
      # the <tt>:status</tt> option.  This status action must match the one expected
      # in the +form_tag_with_upload_progress+ helper.
      #
      def upload_status_for(*actions)
        after_filter :finish_upload_status, :only => actions
        
        define_method(actions.last.is_a?(Hash) && actions.last[:status] || :upload_status) do
          render(:inline => '<%= upload_progress_status %>', :layout => false)
        end
      end
    end

    # Overwrites the body rendered if the upload comes from a form that tracks
    # the progress of the upload.  After clearing the body and any redirects, this
    # method then renders the helper +finish_upload_status+
    #
    # This method only needs to be called if you wish to pass a
    # javascript parameter to your finish event handler that you optionally
    # define in +form_with_upload_progress+
    #
    # === Parameter:
    #
    # client_js_argument:: a string containing a Javascript expression that will
    #                      be evaluated and passed to your +finish+ handler of
    #                      +form_tag_with_upload_progress+.
    #
    # You can pass a String, Number or Boolean.
    #
    # === Strings
    #
    # Strings contain Javascript code that will be evaluated on the client. If you 
    # wish to pass a string to the client finish callback, you will need to include 
    # quotes in the +client_js_argument+ you pass to this method.
    #
    # ==== Example
    #
    #   finish_upload_status("\"Finished\"")
    #   finish_upload_status("'Finished #{@document.title}'")
    #   finish_upload_status("{success: true, message: 'Done!'}")
    #   finish_upload_status("function() { alert('Uploaded!'); }")
    #
    # === Numbers / Booleans
    #
    # Numbers and Booleans can either be passed as Number objects or string versions 
    # of number objects as they are evaluated by Javascript the same way as in Ruby.
    #
    # ==== Example
    #
    #   finish_upload_status(0)
    #   finish_upload_status(@document.file.size)
    #   finish_upload_status("10")
    #
    # === Nil
    #
    # To pass +nil+ to the finish callback, use a string "undefined"
    #
    # ==== Example
    #
    #   finish_upload_status(@message || "undefined")
    #
    # == Redirection
    #
    # If you action performs a redirection then +finish_upload_status+ will recognize
    # the redirection and properly create the Javascript to perform the redirection in
    # the proper location.
    #
    # It is possible to redirect and pass a parameter to the finish callback.
    #
    # ==== Example
    #
    #   redirect_to :action => 'show', :id => @document.id
    #   finish_upload_status("'Redirecting you to your new file'")
    #
    #
    def finish_upload_status(client_js_argument='')
      if not @rendered_finish_upload_status and params[:upload_id]
        @rendered_finish_upload_status = true

        erase_render_results
        location = erase_redirect_results || ''

        ## TODO determine if #inspect is the appropriate way to marshall values
        ## in inline templates

        template = "<%= finish_upload_status({"
        template << ":client_js_argument => #{client_js_argument.inspect}, "
        template << ":redirect_to => #{location.to_s.inspect}, "
        template << "}) %>"

        render({ :inline => template, :layout => false })
      end
    end
 
    # Returns and saves the next unique +upload_id+ in the instance variable
    # <tt>@upload_id</tt>
    def next_upload_id
      @upload_id = last_upload_id.succ
    end

    # Either returns the last saved +upload_id+ or looks in the session
    # for the last used +upload_id+ and saves it as the intance variable
    # <tt>@upload_id</tt>
    def last_upload_id
      @upload_id ||= ((session[:uploads] || {}).keys.map{|k| k.to_i}.sort.last || 0).to_s
    end

    # Returns the +upload_id+ from the query parameters or if it cannot be found
    # in the query parameters, then return the +last_upload_id+
    def current_upload_id
      params[:upload_id] or last_upload_id
    end
    
    # Get the UploadProgress::Progress object for the supplied +upload_id+ from the
    # session. If no +upload_id+ is given, then use the +current_upload_id+
    #
    # If an UploadProgress::Progress object cannot be found, a new instance will be
    # returned with <code>total_bytes == 0</code>, <code>started? == false</code>, 
    # and <code>finished? == true</code>.
    def upload_progress(upload_id = nil)
      upload_id ||= current_upload_id
      session[:uploads] && session[:uploads][upload_id] || UploadProgress::Progress.new(0)
    end

    # == THIS IS AN EXPERIMENTAL FEATURE
    #
    # Which means that it doesn't yet work on all systems. We're still working on full
    # compatibility. It's thus not advised to use this unless you've verified it to work
    # fully on all the systems that is a part of your environment. Consider this an extended
    # preview.
    #
    # Upload Progress abstracts the progress of an upload.  It's used by the
    # multipart progress IO that keeps track of the upload progress and creating
    # the application depends on.  It contians methods to update the progress
    # during an upload and read the statistics such as +received_bytes+,
    # +total_bytes+, +completed_percent+, +bitrate+, and
    # +remaining_seconds+
    #
    # You can get the current +Progress+ object by calling +upload_progress+ instance
    # method in your controller or view.
    #
    class Progress
      unless const_defined? :MIN_SAMPLE_TIME
        # Number of seconds between bitrate samples.  Updates that occur more
        # frequently than +MIN_SAMPLE_TIME+ will not be queued until this
        # time passes.  This behavior gives a good balance of accuracy and load
        # for both fast and slow transfers.
        MIN_SAMPLE_TIME = 0.150

        # Number of seconds between updates before giving up to try and calculate
        # bitrate anymore
        MIN_STALL_TIME = 10.0   

        # Number of samples used to calculate bitrate
        MAX_SAMPLES = 20         
      end

      # Number bytes received from the multipart post
      attr_reader :received_bytes
      
      # Total number of bytes expected from the mutlipart post
      attr_reader :total_bytes
      
      # The last time the upload history was updated
      attr_reader :last_update_time

      # A message you can set from your controller or view to be rendered in the 
      # +upload_status_text+ helper method.  If you set a messagein a controller
      # then call <code>session.update</code> to make that message available to 
      # your +upload_status+ action.
      attr_accessor :message

      # Create a new Progress object passing the expected number of bytes to receive
      def initialize(total)
        @total_bytes = total
        reset!
      end

      # Resets the received_bytes, last_update_time, message and bitrate, but 
      # but maintains the total expected bytes
      def reset!
        @received_bytes, @last_update_time, @stalled, @message = 0, 0, false, ''
        reset_history
      end

      # Number of bytes left for this upload
      def remaining_bytes
        @total_bytes - @received_bytes
      end

      # Completed percent in integer form from 0..100
      def completed_percent
        (@received_bytes * 100 / @total_bytes).to_i rescue 0
      end

      # Updates this UploadProgress object with the number of bytes received
      # since last update time and the absolute number of seconds since the
      # beginning of the upload.
      # 
      # This method is used by the +MultipartProgress+ module and should
      # not be called directly.
      def update!(bytes, elapsed_seconds)#:nodoc:
        if @received_bytes + bytes > @total_bytes
          #warn "Progress#update received bytes exceeds expected bytes"
          bytes = @total_bytes - @received_bytes
        end

        @received_bytes += bytes

        # Age is the duration of time since the last update to the history
        age = elapsed_seconds - @last_update_time

        # Record the bytes received in the first element of the history
        # in case the sample rate is exceeded and we shouldn't record at this
        # time
        @history.first[0] += bytes
        @history.first[1] += age

        history_age = @history.first[1]

        @history.pop while @history.size > MAX_SAMPLES
        @history.unshift([0,0]) if history_age > MIN_SAMPLE_TIME

        if history_age > MIN_STALL_TIME
          @stalled = true
          reset_history 
        else
          @stalled = false
        end

        @last_update_time = elapsed_seconds
        
        self
      end

      # Calculates the bitrate in bytes/second. If the transfer is stalled or
      # just started, the bitrate will be 0
      def bitrate
        history_bytes, history_time = @history.transpose.map { |vals| vals.inject { |sum, v| sum + v } } 
        history_bytes / history_time rescue 0
      end

      # Number of seconds elapsed since the start of the upload
      def elapsed_seconds
        @last_update_time
      end

      # Calculate the seconds remaining based on the current bitrate. Returns
      # O seconds if stalled or if no bytes have been received
      def remaining_seconds
        remaining_bytes / bitrate rescue 0
      end

      # Returns true if there are bytes pending otherwise returns false
      def finished?
        remaining_bytes <= 0
      end

      # Returns true if some bytes have been received
      def started?
        @received_bytes > 0
      end

      # Returns true if there has been a delay in receiving bytes.  The delay
      # is set by the constant MIN_STALL_TIME
      def stalled?
        @stalled
      end

      private
      def reset_history
        @history = [[0,0]]
      end
    end
  end
end